In an active matrix organic light emitting diode (AMOLED), light emission is driven by a saturation current generated by a driving transistor. Driving transistors with different threshold voltages Vth, even when inputted with a same input grayscale voltage, may produce saturation currents having different values for driving the AMOLED. For example, a low temperature polysilicon (LTPS) driving transistor-based AMOLED display panel typically has poor threshold voltage uniformity throughout the display panel. Moreover, the threshold voltage Vth typically drifts over time in such a display panel. All these issues contribute to non-uniformity in display brightness throughout the display panel.
As shown in FIG. 1, a conventional pixel driving circuit includes a first transistor T1, a second transistor T2, a third transistor T3, a fourth transistor T4, a fifth transistor T5, a sixth transistor T6, a seventh transistor T7, a first capacitor C1, and an OLED. EM is an input port for emitting light control signal. G is an input port for data write-in control signal. Vdata is a data voltage signal. Vinit is an initialization voltage signal. Re is an input port for the initialization control signal. T3 is the driving transistor. A source of T3 is received a high voltage level VDD and a drain of T3 is connected to an anode of OLED via the sixth transistor T6. A cathode of the OLED is received a low voltage level VSS. Referring to FIG. 1, the first capacitor C1 is connected between a gate of T3 and a second terminal of T7. A first terminal of T5 and a first terminal of T7 are commonly connected to a reference voltage input port configured to receive a reference voltage Vref. When the pixel driving circuit is operated by coupling to a high voltage level VDD, a parasitic capacitance between the gate and source of T3 may affect the gate voltage level of the driving transistor. As a result, the gate voltage level of the driving transistor cannot be maintained at a stable value.